The present invention relates generally to measurement systems, and more particularly, to non-contact measuring of rolled, calendared, woven, extruded, and other sheet and web products. The invention incorporates an electromagnetic radiation emitter, an electromagnetic radiation receiver, and a measurement processing unit.
There are many situations in industrial process control where the continuous, accurate measurement of product width, thickness, or edge position can improve the quality and efficiency of the production process. There are only a few known methods for making some of these measurements. For example, in the primary metals industry, the most common methods involve the use of charge coupled device (CCD) television cameras with elaborate mounting devices and expensive computer support systems. Other methods involve mechanically scanned laser beams and mechanically positioned opto-electronic devices. The mechanically positioned devices generally require frequent maintenance in the industrial environment while the scanned laser devices also have moving parts that wear out and require unscheduled down time or scheduled periodic maintenance.
In the CCD camera systems, a small change in the position of the camera is multiplied by the magnification of the lens in such systems. If the lens if focusing the view of a 40 inch wide strip, for example, on to a 1 inch long array, a change in the position of the camera of a few thousands of an inch is multiplied by a factor of 40 as the image position shifts on the array. The thermal growth in the lengthy of mounting fixture support arms must be compensated for if accurate position measurements are to be made with such a system. Thus, the elaborate fixtures that are required for such systems, and the installation and computer support needed, often make the cost of CCD camera systems prohibitive.
Materials undergoing industrial production processes vary widely in physical makeup, such as extruded plastics or steel billets. Speed of movement of these materials as they are being processed also varies widely. Some processes may move a work piece at a very slow rate of speed while other processes may move a work piece at speeds of upwards to 90 mph. Some materials will also reach extremely high temperature. This must be taken into consideration where measurement devices could potentially be destroyed by such temperatures.
One measurement system which has found substantial acceptance in industry is marketed under the trademark "SCAN-A-LINE.RTM.". The SCAN-A-LINE.RTM. measurement system employs a linear array of electromagnetic radiation emitting diodes positioned on one side of a material, such as a web or sheet moving within a production process. The diodes of the array are illuminated in a scanning sequence having a stable time base, for example, at a 20 KHZ rate developed by a quartz crystal oscillator. Positioned above the moving material under production and opposite the associated diode array, is a tuned photoresponsive receiver which reacts to the illumination emanating from the diodes which are unblocked or partially blocked from view by the receiver by the moving material. Associated controls connected to the receiver are called upon to extrapolate the electromagnetic radiation signals to develop measurement information concerning the material. The extrapolation is based upon the observation that each LED in the emitting array produced a cone of electromagnetic radiation, and the electromagnetic radiation cones from adjacent LEDs overlap in the electromagnetic radiation path to the receiver. An edge of the product being measured blocking the electromagnetic radiation path from the emitting diodes to the receiver will attenuate the electromagnetic radiation from more than one diode. The extrapolating process takes samples of the amplitude of the electromagnetic radiation received in sequence from the partially blocked and unblocked LEDs, and develops a time-based stair step electromagnetic radiation output pattern representing scan across the edge. The edge position of the material being observed may then be defined as the time equivalent point on the smooth curve signal where the voltage drops to one-half of the peak LED signal amplitude. The SCAN-A-LINE.RTM. system is marketed by Harris Instrument Corporation of Columbus, Ohio.
The SCAN-A-LINE.RTM. system was first patented in U.S. Pat. No. 5,220,177, which issued on Jun. 15, 1993. The patent described a system wherein each electromagnetic radiation emitting device of the array utilized is energized by a unique drive current which is preselected to cause the emission of electromagnetic radiation exhibiting substantially uniform intensity at the receiver when there is no attenuation of the electromagnetic radiation by a material under edge evaluation. Such balancing or optimization of the array electromagnetic radiation output not only achieves importantly enhanced system accuracy in carrying out edge location, but also substantially expands the range of application for such non-contacting measurement techniques. In this regard, the edge locating technique can be employed with transparent or semi-transparent materials. When so employed, the time based trigger signal from which edge data is developed in generated at a location in scan time between a transition of detected amplitudes representing a maximum value and a minimum value. System accuracy is substantially improved through the utilization of a receiving photodetector assembly having a lengthwise dimension which is expanded. With the combination of this improved receiving approach and the balanced electromagnetic radiation values at the receiver, system performance has been observed to be improved beyond what would have been expected.
Many of today's industrial measurement applications require measurements of width or position of a product having an unstable passline. Measurement of the instability of passlines has gained in importance. Furthermore, measurement of the width of a material work piece and the thickness of the workpiece are of significant importance in today's industrial process applications. Through the employment of semiconductor device based arrays emitting in the infrared region of the electromagnetic spectrum in conjunction with silicone photocell receiver components, substantially expanded stand-off distances and spacing between the receivers and emitter, are available. Enhanced spacing permits improved edge detection of hot materials such as steel billets. The improved ray trace geometry achieved with enhanced emitter-to-receiver spacing achieves enhanced edge location accuracy at the passline where vertical movement of the material may be encountered. Ray trace geometry further permits an advantageous lower outside edge detection where the edges of relatively thick material forms such, as billets of steel, are monitored.
With the apparatus of the present invention, multiple receivers may be employed with one or more emitters. The receivers may be removed to locations directly over each end of a strip emitter. This arrangement helps to eliminate passline errors. In the present invention, preferably two receivers are used for each emitter and each receiver is located over one of the opposite ends of the emitter. In this manner, a signal can be developed that represents passline height. The passline height signal can effectively be used to correct width measurements for height changes. Thus, the present invention is a system of binocular vision measurement.
By scanning the electromagnetic radiation emitted from an array in a controlled sequence, with a workpiece positioned between the electromagnetic radiation emitting source and at least two receivers, several important measurements can be made concerning the workpiece, as the workpiece moves through a production process. In accordance with the present invention, an array of spaced discrete electromagnetic radiation emitting devices are disposed generally along an array axis. Each electromagnetic radiation emitting device is responsive to the application of a drive current thereto to emit electromagnetic radiation. The electromagnetic radiation array is positioned a select distance from one side of a material workpiece and is located to extend outwardly from at least one edge of the workpiece. At least two photoresponsive receivers are positioned at a predetermined stand-off distance from the material workpiece, in electromagnetic radiation receiving relationship with the array, and oriented so as to position a photodetector axis in substantially parallel relationship with the array axis as each electromagnetic radiation emitting device is discretely energized in a sequence by the application of drive current at a predetermined system frequency. The photodetectors detect the electromagnetic radiation emitted by the electromagnetic radiation emitting devices which are either partially attenuated or nonattenuated by the material workpiece. From the electromagnetic radiation detection, the present invention enables the derivation of output signals at the system frequency which exhibits amplitude data. By correlating the amplitude data with time and space location data, to derive a signal representing a desired measurement concerning the material workpiece.
The present invention comprises the apparatus and method possessing the construction, combination of elements, arrangement of parts and steps which are exemplified in the following drawings and detailed description.